Starbucks (SBUX) doesn't break out drive-thru revenues, but the chain operates approximately 2,650 drive-thru locations, representing approximately 35% of company-operated stores in the US and Canada combined

If fast-food outlets were to close their drive-thru windows, they'd be doing shareholders a major disservice.

But, if certain folks in Washington had their druthers, drive-thrus would go the way of Tara Reid's film "career" and disappear forever, never to be heard from again. It seems the Sierra Club has pinpointed a new cause of total planetary destruction, known as the drive-thru.

According to their estimates, people idling in cars while they wait at drive-thru windows burn around 50 million gallons of gasoline a year, or 0.7 gallons an hour -- hardly even enough to register on the radar of a company like Exxon Mobil (XOM).

The good people at the Sierra Club point out that "the average McDonald's drive-through wait is 159 seconds, [so] we can calculate that the company's consumers burn some 7.25 million gallons of gas each year. The figure for the entire US fast-food industry? Roughly 50 million gallons." The club contends that expansion by fast food chains in China and India will boost that burn rate to 30 billion gallons a year.

These worries have sparked a mad dash to rid municipalities across North America of drive-thrus.

A few examples:

Barry Jacobs, a county commissioner in Hillsborough, North Carolina, proposed a ban on all new drive-thru construction.

San Juan Capistrano, California, banned all construction of new drive-thru windows for eight years, until the policy was partially reversed just a few weeks ago.

In Salt Lake City, a group called Utah Physicians for a Healthy Environment has called for all drive-thru windows to be shut down on days when there's a high concentration of ozone in the air.

And north of the border, the city of London, Ontario is considering a moratorium on new drive-thru construction.

However, Melva Sine, president and CEO of the Utah Restaurant Association says turning a car off and later restarting it creates more emissions than idling.

Greg Beato, writing in The Smart Set, an independent online magazine produced in partnership with Drexel University, concurs, pointing out that "outlets without drive-thrus produced about 40 to 70 percent more smog pollutants and carbon monoxide and 10 to 30 percent more greenhouse gases than the ones that had them. The reason? Idling that occurs in the parking lot as drivers hunt and wait for spaces, the extra distance traveled during this process, and the extra engine start-up that's required after customers complete their transactions and return to their vehicles."

Did the Sierra Club rush to judgment in its analysis of drive-thrus?

In an interview with Minyanville, Bill Bush of the American Petroleum Institute said:

"As a general principle, it's important to take care when you do these different kinds of analyses and to be careful and thorough. If you don't, and your analysis is off-base, you may be causing more harm than good."

Oopsie -- it seems that the Sierra Club wasn't as careful and thorough as they might have been.

Beato offers as evidence a study the Tim Hortons (THI) chain commissioned from a Guelph, Ontario, engineering firm that found the following:

Overall, the findings for the Tim Hortons stores examined in this study indicate no air quality benefit to the public from eliminating drive-thrus.

For a Tim Horton's store with no drive-thru, the congestion that occurs in the parking lot, together with the start-up emissions and emissions from the extra travel distance to get to and from a space, all contribute to produce somewhat higher emissions per vehicle compared to a store that has a drive-thru. This is particularly true in the case of smog pollutants and carbon monoxide but is also true for greenhouse gases.

To put drive-thrus into perspective, combined emissions generated from all vehicles using a drive-thru facility during a peak-hour of operation are relatively small in relation to other common emission sources: smog pollutant emissions from all vehicles are comparable to a single chain saw operating for one hour; CO2 emissions are comparable to a single bus operating for one hour; emissions from all vehicles using a store with a drive-thru during the peak hour are less than one-fifth of the emissions at an urban intersection; and emissions of smog pollutants and greenhouse gases from a single vehicle using a drive-thru are less than 10% and 5%, respectively, of a typical morning commute.

So, don't let guilt get the better of you next time you cruise up to a drive-thru window for a Whopper.

Though, if you do (and you happen to be in the Trenton, NJ, area), there's a quick and easy way to cleanse yourself:

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